Triangle Hazelnut Treats

Prepare a baking tray measuring 12x14 inches (30x35 cm).
Mix 1 3/4 cups (230 g) flour with baking powder. In another bowl, cream together softened butter, sugar, and vanilla sugar. Add eggs and mix again. Then add flour mixed with baking powder and knead the dough. If needed, add 1 tablespoon (20 g) more flour, depending on the size of the eggs; I found 1 3/4 cups (230 g) to be enough. The dough is very nice to work with.
For the filling, melt butter, sugar, vanilla sugar, and milk in a saucepan. Bring to a boil and immediately remove from heat. Stir in hazelnuts. Set aside to cool for about 10 minutes while you roll out the dough. (I ground the hazelnuts in a food processor - 1 1/4 cups (150 g) finely and the remaining 3/4 cup (100 g) coarsely. Do not grind too coarsely so that larger pieces of hazelnuts don't interfere when cutting the triangles.)
Lightly dust a sheet of parchment paper and roll out the dough to fit the prepared baking tray. Transfer the dough to the tray along with the parchment paper and spread jam over it.
Evenly spread the filling over the dough. Bake in a preheated oven at 350°F (180°C) for 20-25 minutes.
After baking, let the cake cool, then cut it into squares measuring 2.5x2.5 inches (6x6 cm). Cut diagonally to form triangles.
For the glaze, melt chocolate with oil and dip both sharp corners of the triangles into the chocolate. Arrange the treats on a plate or tray lined with parchment paper. Place the cookies in the refrigerator for about 20 minutes to let the chocolate set, then serve.